A push-in type sliding door apparatus is one wherein the sliding doors are flush, on the interior side, with the fixed wall of the vehicle when the doors are in their closed position. During opening movement, each door is pulled away from the fixed wall of the vehicle by a certain distance to avoid either the fixed wall or another closed door, and then it is pulled to the open position where it is over the outer side of the fixed wall or the other door.
In one such conventional opening and closing mechanism, as exemplified by Japanese Patent Publication No. SHO. 57-59095, the sliding doors are shifted by a required distance outwardly away from the vehicle's wall by means of turning rails which are separately provided in addition to the travel rails. In this mechanism, each sliding door is provided with shafts and crank arms, and the door is pulled outwardly by the length of the upper and the lower crank arms to open it. This structure requires two sets of opening and closing mechanisms, and the door cannot be easily handled by an operator.
On the other hand, the mechanism disclosed by Japan Patent Provisional Publication No. SHO. 57-165571 improved on the above-mentioned mechanism of a crank shaft, crank arms and arm rollers to reduce the required structure to one set of the mechanism per door, and with some arrangements of the rails and door rollers, the pushing-in and pulling-out operations are effected by turning a crank shaft. The mechanism, however, has some disadvantages including that the mechanism is complex and cannot be fabricated with ease, and that the two-stage construction of the upper horizontal door roller reduces the effective height of the opening.
It is a general object of the present invention to eliminate such disadvantages of the prior art mechanisms and to provide a push-in type sliding door apparatus and a locking mechanism therefor that are simple in construction and ensure reliable opening and closing operations.